Periodic Reporting for period 2 - SHARP (SHocks: structure, AcceleRation, dissiPation)
Période du rapport: 2022-01-01 au 2023-12-31
Shock waves are present in air and water on Earth and a wide range of plasmas in the universe. These plasmas are generally collisionless. The EU-funded SHARP project contributed significantly to understanding of the structure of collisionless shocks in diverse environments and the acceleration processes at all shock stages. The project have exploited the heliospheric data and performed an inclusive comparative analysis of the Earth bow and planetary and interplanetary shocks. SHARP combined the findings from in situ measurements of heliospheric and supernovae remnant shocks with remote observation of distant astrophysical shocks. The project developed a high-level database of shocks and innovative instruments for the shock analysis.
The overall aim of the SHARP project was to advance our understanding of the collisionless shock structure, the physics of charged particle acceleration and heating, and collisionless dissipation in collisionless shocks across a range of scales in the Universe. SHARP efforts have been targeted to the thorough analysis of data for the terrestrial bow shocks from Cluster and MMS missions, interplanetary shocks with THEMIS/ARTEMIS missions, planetary shocks on Mercury from Messenger spacecraft, shocks on non-magnetized planets Venus and Mars with VEX and MAVEN missions, and supernova remnant shocks using remote observations by Imaging X-ray Polarimetry Explorer (IXPE) satellite. This data analysis has been done in a close, day-to-day collaboration and joint work between all the SHARP partners. The analysis of whistler waves in the shock foot established their connection to the reflected ions. Time-dependent rippling has been studied theoretically and observationally. Multiple ion phase space holes were identified as a major signature of rippling. In order to advance our understanding of the key issues related to the acceleration of particles at CSs, downstream distributions in supercritical shocks have been extensively analyzed. It was shown that non-Maxwellian tails lead to enhanced reflection. For the first time, ion kinetics at the shock ramp was connected to the Rankine-Hugoniot relations. In order to understand particle acceleration at astrophysical shocks, the focus was on the issues of magnetic-field turbulence around supernova remnant (SNR) shocks. The important result is that the downstream region in an SNR shock is highly turbulent, which impacts both the X-ray polarization and radiative outcome. Observationally, it is difficult to compare one to one heliospheric and astrophysical shocks. Nevertheless, the issue of radially stretching of magnetic field downstream of the shock could be probed closer to the shock in heliospheric shocks. One common parameter to be investigated is the issue of electron versus proton(ion) temperature. An extensive statistical analysis of the downstream electron-to-proton temperature ratio on MMS observed shocks has been performed and compared with the inferred ratios at SNR shocks. The project produced a centralized shock database with straightforward access to it via https://sharp.fmi.fi/shock-database/ for efficient exploitation of data. The SHARP shock database contains information about terrestrial shocks, interplanetary shocks and shocks at non-magnetized planets (Venus and Mars). The database consolidates the information on the shock crossings, and provides a number of the shock parameters (dependent on the available measurements in corresponding regions) and corresponding shock plots and/or quicklook plots. The efforts within SHARP project resulted in 45 papers (all published as open access), publications were promoted on @FMIspace twitter. The results were also presented in 37 presentations at international conferences. SHARP video was produced using Apogee company and placed on twitter and youtube by all partners. SHARP consortium organised the SHARP Summer School on Collisionless Shocks in Space in Levi, Finland, August 21-25, 2023. The school included lectures and lab sessions. The school participants consisted of 23 students from 12 different countries. In addition, dissemination material was created for the summer school. Each student received a canvas bag customized with the SHARP logo and a custom pen with the SHARP web page address (sharp.fmi.fi). All lectures and lab materials are available at SHARP website. Topics of SHARP (including SHARP video) are now a part of the “Plasma physics” course for graduates in BGU. SHARP in general was presented to a general public in lectures during multidisciplinary theme week in science and technology at the University of Uppsala, at the Bitopia museum in September 2022 in Uppsala as part of the Astronomy Day and Night.
The state of art before SHARP resembled a puzzle which consisted of a number of disconnected assembled parts. For example, the structure of low-Mach number shocks was deduced from the observations at the Earth bow shock, but the theory has not been verified at other planetary shocks. Certain features of high-Mach number shocks have been deduced from observations, but no theory existed which would explain the features and their dependence on the Mach number. Certain understanding of the very high Mach shock physics, as inferred from remote observations of supernova remnants shocks, and in situ observations of heliosperic shocks were poorly connected. On the other hand, the amount of the available data collected in the heliosphere and in remote astrophysical observations is well beyond the capabilities of single researchers or even single groups. The research done in SHARP project has successfully validated the theory of low-Mach number shock structure, developed for the terrestrial bow shock, to other low-Mach number shocks. SHARP achieved a big leap in understanding the shock structure and particle energization in shocks, by extending theory to high-Mach shocks, thus building a bridge connecting the heliospheric and astrophysical shocks. The shock database is developed and filled with the data on shocks in a wide range of parameters. The shock database significantly contributes to the “exploitation of space data sets collected by European and international missions”. The database consists of thousands of terrestrial and non-terrestrial shock crossings. Thus, this exploits existing datasets and is expected to facilitate numerous new studies of collisionless shocks both of a statistical nature as well as detailed case studies.